CD lens scratches

[N_Cook]

The platter shifted along the spinner motor shaft until the lens could touch
CDs so scratched CDs and presumably, as convex top side, scratched lens. Has
never read the TOC with any sacrificial CDs of mine.
I cannot turn the lens in the lens carrier but the scratches , under x30 ,
seem to be not linear as I'd expect but look like matted micro cotton wool,
ie curvy. How is that possible from a spinning CD. Is it that the CD grabs
the lens on its floppy suspension and twists the housing enough to produce
curves.
Is there some sort of home-chemistry optical conformal coating .
Even if the coating works only when wet , just to confirm a lens problem out
of interest.
Not worth replacing the deck ,but has anyone robbed a lens from a scrapped
different make/type of deck and transplanted an as-you-find-it lens ,only ,
to make a goer?

 

[N_Cook]

To answer the last question first, I have taken lenses from lasers on scrap
decks on a number of occasions, and had a good degree of success. Most
notably, with Pioneer lasers that are mounted upside down, and which the
lenses regularly fall out of, and then are lost, presumably through
ventilation slots. Some of course, are still rattling around inside the
player, but often they are not. I have used lenses from whatever came to
hand that was the right diameter and general shape - mostly lenses from Sony
KSS series lasers. The 'trick' is to make sure that *all* glue is carefully
removed from both the lens suspension, and the underside of the lens rim.
The lens *must* lie absolutely flat before it is re-fixed. I do this by
putting the tiniest drop of superglue on the end of a sharply pointed thin
scalpel blade, and then - whilst holding the lens pressed down with a cotton
bud - touch it to the edge. The superglue is 'wicked' into the gap by
capillary action, and sets very quickly because the layer is so thin. Once
it has set, I repeat for the gap 180 degrees away. Sometimes, although not
always, it is necessary to perform a set-up of focus offset. This is, of
course, possible with a Pioneer, as it has a full raft of adjustments
available, and clear test points and procedures for setting them. On late
generation players, that have no such adjustments, it may be more of a
problem, although some have automatic in-software adjustments.

On home chemistry for getting rid of the scratches, I have found that the
oil in metal polish wadding - such as Duraglit - has a very similar
refractive index to the plastic used to make CDs from. So much so that
scratches - even deep ones - disappear like magic when the disc is first
treated to a wipe of wadding, left to go white, and then polished up with a
dry cloth. I have always assumed that the oil in the wadding 'fills' the
scratches in. It actually lasts quite a long time. Might be worth trying
this with your scratched lens ? As it is made from optically-clear plastic,
I would guess that it will not be too dissimilar from that which is used to
make the discs.

On the nature of the scratches, I would be extremely disinclined to believe
that this had been done by anything coming between the disc and lens. For a
start, the 'wall' around the edge of most lenses is at least as tall as the
convex centre of the lens, and possibly taller. I have known lasers to
scratch the underside of a disc, but never come across corresponding damage
back the other way. I would suspect that someone has either 'had a go' at
cleaning the lens manually, using inappropriate technique and materials /
chemicals, or possibly used one of those dreadful cleaning discs with
bristles on the bottom ...

Arfa

Some useful stuff there. With a needle lifting the lens carrier it will rise
to the level of the underlying deck, combined with some inertia in such a
flimsey mechanism, I could quite see the lens hitting a CD that is
erroneously spinning only just above that level.
The scratches are otherwise in a neat circle around the central area of the
lens only , so unlikely done by a hand.
Duraglit sounds a bit drastic , doesn't it have jeweller's rouge or some
abrasive in it? but as useless as it stands then nothing to loose , now to
see if I can dislodge the lens without destroying the suspension frame

 

[Mark Zacharias]

Some useful stuff there. With a needle lifting the lens carrier it will
rise
to the level of the underlying deck, combined with some inertia in such a
flimsey mechanism, I could quite see the lens hitting a CD that is
erroneously spinning only just above that level.
The scratches are otherwise in a neat circle around the central area of
the
lens only , so unlikely done by a hand.
Duraglit sounds a bit drastic , doesn't it have jeweller's rouge or some
abrasive in it? but as useless as it stands then nothing to loose , now to
see if I can dislodge the lens without destroying the suspension frame

I think the circular rim of the lens prevents this. The dome shape of the
lens is still below the height of the outer rim, I_think_

I would just clean it and it's likely OK.

Generally if a disc tilts, it scrapes the tray or some other part well
before it can touch the lens assembly.

Mark Z.

 

[N_Cook]

I think the circular rim of the lens prevents this. The dome shape of the
lens is still below the height of the outer rim, I_think_

I would just clean it and it's likely OK.

Generally if a disc tilts, it scrapes the tray or some other part well
before it can touch the lens assembly.

Mark Z.

I can pull this lens suspension up and it stops with top of dome perhaps
..5mm above the underlying deck area and has no protection ring, add in some
inertia to the kicks and and I'm pretty sure it would be hitting any CD once
the platter had dropped on the motor spindle. I will try jigging/temporary
ancjoring the lens into that posistion to work on, as to get to it otherwise
looks as though you have to take the whole laser assembly apart or at least
a number of set screws that are adjustments of some sort by the look of
them.